In a general electrophotographic process, an electrophotographic photoreceptor undergoes processes including at least cleaning, charging, light exposure, development, and image transfer. The process employs a cleaning blade for removing toner remaining on the surface of a photoreceptor drum, a conductive roller for uniformly imparting electric charge to the photoreceptor, a transfer belt for transferring a toner image, and the like. From the viewpoints of plastic deformation and wear resistance, the cleaning blade is usually produced from a thermosetting polyurethane resin.
However, when a cleaning blade formed of a polyurethane resin is employed, the friction coefficient between the blade member and a photoreceptor drum increases, and delamination of the blade and anomalous sound problematically occur. Also, the driving torque of the photoreceptor drum must be increased in some cases. Furthermore, the edge of the cleaning blade may be caught by a photoreceptor drum or another member, whereby the cleaning blade is stretched or cut, and the edge of the cleaning blade is broken due to wear. These problems become severe particularly when the cleaning blade has low hardness. As a result, the durability of the cleaning blade may be impaired.
In order to solve the aforementioned problems, the contact portion of a polyurethane blade has been modified to have high hardness and low friction. In one proposed procedure, a polyurethane blade is impregnated with an isocyanate compound, to thereby induce reaction between the polyurethane resin and the isocyanate compound, whereby the hardness is enhanced at only the surface or a portion near the surface of the polyurethane resin blade, and friction of the surface is reduced (see, for example, Patent Documents 1 to 3).
However, when characteristics required for such a blade are attained through methods disclosed in Patent Documents 1 to 3, the polyurethane resin blade must be impregnated with a surface treatment liquid containing an isocyanate compound at high concentration. In this case, the treated surface layer (hereinafter may be referred to as a surface treatment layer) must be formed to a considerable depth. When a high-concentration surface treatment liquid is used, and a thick surface treatment layer is formed, an excessive amount of isocyanate tends to remain on the surface of the blade, thereby requiring an additional step of removing the excessive isocyanate. In contrast, when the thickness of the surface treatment layer is reduced, wear resistance decreases, thereby problematically impairing cleaning performance.